Michal Hocko wrote: > On Sat 07-10-17 20:30:19, Tetsuo Handa wrote: > [...] > > >From 6a0fd8a5e013ac63a6bcd06bd2ae6fdb25a4f3de Mon Sep 17 00:00:00 2001 > > From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> > > Date: Sat, 7 Oct 2017 19:29:21 +0900 > > Subject: [PATCH] virtio: avoid possible OOM lockup at virtballoon_oom_notify() > > > > In leak_balloon(), mutex_lock(&vb->balloon_lock) is called in order to > > serialize against fill_balloon(). But in fill_balloon(), > > alloc_page(GFP_HIGHUSER[_MOVABLE] | __GFP_NOMEMALLOC | __GFP_NORETRY) is > > called with vb->balloon_lock mutex held. Since GFP_HIGHUSER[_MOVABLE] > > implies __GFP_DIRECT_RECLAIM | __GFP_IO | __GFP_FS, despite __GFP_NORETRY > > is specified, this allocation attempt might depend on somebody else's > > __GFP_DIRECT_RECLAIM memory allocation. > > How would that dependency look like? Is the holder of the lock doing > only __GFP_NORETRY? __GFP_NORETRY makes difference only after reclaim attempt failed. Reclaim attempt of __GFP_DIRECT_RECLAIM | __GFP_IO | __GFP_FS request can indirectly wait for somebody else's GFP_NOFS and/or GFP_NOIO request (e.g. blocked on filesystem's fs lock). And such indirect GFP_NOFS and/or GFP_NOIO request can reach __alloc_pages_may_oom() unless they also have __GFP_NORETRY. And such indirect GFP_NOFS and/or GFP_NOIO request can call OOM notifier callback and try to hold balloon_lock at leak_balloon() which fill_balloon() has already held before doing GFP_HIGHUSER[_MOVABLE] | __GFP_NOMEMALLOC | __GFP_NORETRY request. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
